What is the Difference Between a

Chemical Change and a Physical

Change?

Physical Change

Physical changes occur when objects undergo a change that does not change their chemical nature. A physical change involves a change in physical properties. Physical properties can be observed without changing the type of matter. Examples of physical properties include: texture, shape, size, color, odor, volume, mass, weight, and density.

Examples of a Physical Change

• Piece of paper ---- Rip It ---- Still a Piece of paper

Chemical Change

Chemical changes are changes substances undergo when they become new or different substances. For example, the fireworks we see on the 4th of July are actually metals such as magnesium and copper that change chemically as they light up the night skies with their fantastic colors. To identify a chemical change look for observable signs such as color change, bubbling and fizzing, light production, smoke, and presence of heat.

Click on the candle and observe:

Examples of a Chemical Change

• Perhaps you have found a half eaten apple that turns brown.  The reason is that a chemical change has occurs when food spoils.

Examples of a Chemical Change

• The explosion of fireworks is an example of chemical change

Clues that a Chemical Change Happened

• Odor Changes It only takes one experience with a rotten egg to learn that they smell different that fresh eggs.  When eggs and food spoil, they undergo a chemical change.  The change in odor is a clue to the chemical change

Clues that a Chemical Change Happened

• Production of Gases The formation of a gas is a clue to chemical changes.  The bubbles of gas that you observed form when an antacid is dropped into water is an example of change.

Clues that a Chemical Change Happened

• Production of Gases or Solids Another clue that a chemical change has occurred is the formation of a solid.  A solid that separates out of solution during a chemical change is called a precipitate

Here, sodium iodide (NaI) is added to lead(II) nitrate (Pb(NO3)2). The result is a bright yellow precipitate

Clues that a Chemical Change Happened

• Energy - Absorbed or Released Another sign of a chemical change is the release or gain of energy by an object.  Many substances absorb energy to undergo a chemical change.  Energy is absorbed during chemical changes involved in cooking, like baking a cake.